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Full Discussion: Using read to assign value to bash variable not working
Top Forums UNIX for Beginners Questions & Answers Using read to assign value to bash variable not working Post 303043533 by Chubler_XL on Thursday 30th of January 2020 09:04:36 PM
Old 01-30-2020
This is because commands within a pipeline are run in subshells so the read statement is setting the variables is a subshell which has not impact on the main shell.

You can achieve what you want using process substitution like this:

Code:
# read var1 var2 < <(openstack hypervisor stats show | awk -F'|' 'NR==14{print $2,$3}')
# echo $var1
vcpus

Edit:
Also in bash 4.* and later you can use a shell option to run the last pipeline command in the current shell.
Note this only work for shells without job control, so in an interactive shell (as opposed to a script) you will also need turn off job control (set +m).

Quote:
lastpipe
If set, and job control is not active, the shell runs the last command of a pipeline
not executed in the background in the current shell environment.
Code:
# echo $BASH_VERSION
5.0.7(1)-release
# shopt -s lastpipe
# set +m

# echo A B C | head -1 | read first second rest
# echo $first
A

# set -m
# shopt -u lastpipe

Last edited by Chubler_XL; 01-30-2020 at 10:25 PM..
These 2 Users Gave Thanks to Chubler_XL For This Post:
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LEARN ABOUT SUNOS

readonly

readonly(1)							   User Commands						       readonly(1)

NAME

       readonly - shell built-in function to protect the value of the given variable from reassignment

SYNOPSIS

   sh
       readonly [name...]

   ksh
       **readonly [ name [ = value]...]

       **readonly -p

DESCRIPTION

   sh
       The  given  names  are  marked  readonly and the values of the these names may not be changed by subsequent assignment. If no arguments are
       given, a list of all readonly names is printed.

   ksh
       The given names are marked readonly and these names cannot be changed by subsequent assignment.

       When -p is specified, readonly writes to the standard output the names and values of all read-only variables, in the following format:

       "readonly %s=%s
", name, value

       if name is set, and:

       "readonly $s
", name

       if name is unset.

       The shell formats the output, including the proper use of quoting, so that it is suitable for reinput to the shell as commands that achieve
       the same value and readonly attribute-setting results in a shell execution environment in which:

       1.  Variables with values set at the time they were output do not have the readonly attribute set.

       2.  Variables  that  were  unset  at  the time they were output do not have a value at the time at which the saved output is reinput to the
	   shell.

       On this man page, ksh(1) commands that are preceded by one or two ** (asterisks) are treated specially in the following ways:

       1.  Variable assignment lists preceding the command remain in effect when the command completes.

       2.  I/O redirections are processed after variable assignments.

       3.  Errors cause a script that contains them to abort.

       4.  Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a  vari-
	   able  assignment.  This means that tilde substitution is performed after the = sign and word splitting and file name generation are not
	   performed.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       ksh(1), sh(1), typeset(1), attributes(5)

SunOS 5.10							    17 Jul 2002 						       readonly(1)
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